The Mu-Tron VII was never really produced. It was a prototype which was not yet finished when Musitronics was sold to ARP.

Mike Beigel, the developer of the Mu-Trons

"During the late '70s, the Holy Grail was the guitar synthesizer. We were working on one that was not strictly a synthesizer because it did not use the guitar to control an oscillator to generate the sounds. We tried to make enough sophisticated modifications to the sounds by basically combining sound effects to give the function of a synthesizer and keep the versatility of a guitar sound. We were about 95 percent there, but we would never release a product that was 95 percent. Although a few people saw the product, which was called the Mu-Tron VII and looked like a Bi-Phase with more knobs, we never went into production because at that point we still hadn't perfected it."